1. Technical Field of the Invention
The present invention relates generally to a fuel injector for internal combustion engines, and more particularly to an improved structure of a fuel injector designed to suppress unwanted vibrations of a nozzle needle-actuating piston for avoiding injection of an excess quantity of fuel.
2. Background Art
Hydraulic fuel injectors equipped with a piezoelectric valve actuator are used in internal combustion diesel engines of automotive vehicles. Such a fuel injector includes a large-diameter piston moved by the expansion and contraction of the piezoelectric valve actuator, a pressure chamber filled with hydraulic fluid, and a small-diameter piston which are arranged in alignment with each other. The movement of the large-diameter piston causes the hydraulic fluid in the pressure chamber to change in pressure which moves the small-diameter piston. The small-diameter piston then actuates a control valve.
When it is required to emit a fuel spray, the piezoelectric valve actuator is energized and expands to increase the hydraulic pressure in the pressure chamber through the large-diameter piston. This causes the expansion of the piezoelectric valve actuator to be amplified hydraulically and transmitted to the small-diameter piston. The small-diameter piston then moves downward and opens the control valve. When the control valve is opened, it will cause the pressure in a back pressure chamber to drop, thereby lifting up a nozzle needle to initiate fuel injection. Contracting the piezoelectric valve actuator will cause the small-diameter piston to move upward, thereby closing the control valve to terminate the fuel injection.
The above type of fuel injector, however, has the drawback in that during the contraction of the piezoelectric valve actuator, the control valve may be re-opened to inject an excess fuel into the engine undesirably. This is because the small-diameter piston overshoots due to its inertia when lifted upward and then moves downward as a reaction to open the control valve again. The small-diameter piston is exposed at its end to the pressure chamber and thus continues to oscillate for a relative long period of time. The amplitude of the oscillation increases and decreases cyclically as a function of width of an actuator-energizing pulse signal inputted to the piezoelectric valve actuator, thereby resulting in a change in quantity of fuel injected into the engine. Specifically, the quantity of fuel injected which is changed in proportion to the width of the actuator-energizing pulse signal changes undesirably due to the oscillation of the small-diameter piston.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of a fuel injector which is designed to minimize unwanted vibrations of a nozzle needle-actuating piston for avoiding injection of an excess quantity of fuel.
According to one aspect of the invention, there is provided a fuel injector which comprises: (a) a housing; (b) a control valve disposed movably within the housing to displace a needle for emitting a fuel spray; (c) a large-diameter piston disposed slidabley within the housing; (d) a small-diameter piston disposed slidably within the housing to move the control valve; (e) a displacement amplifying chamber filled with fluid to which the large-diameter piston and the small-diameter piston are exposed, the displacement amplifying chamber working to amplify and transmit displacement of the large-diameter piston to the small-diameter piston; (f) an actuator working to displace the large-diameter piston; and (g) a stopper restricting movement of the small-diameter piston toward the displacement amplifying chamber.
In the preferred mode of the invention, a damper is disposed within the displacement amplifying chamber to suppress vibrations of the small-diameter piston.
The damper is implemented by a hole formed in a ring plate secured or fitted slidably within the displacement amplifying chamber.
The stopper is implemented by a ring plate which is secured in the displacement amplifying chamber with a surface opposed to an end of the small-diameter piston through a given gap.
The housing has formed therein a first cylindrical chamber within which the large-diameter piston is disposed and a second cylindrical chamber within which the small-diameter piston is disposed. The first cylindrical chamber communicates with the second cylindrical chamber through the displacement amplifying chamber. The second cylindrical chamber extends eccentrically to a longitudinal center line of the first cylindrical chamber to define a surface at a junction of the first and second cylindrical chambers which is exposed to the second cylindrical chamber and works as the stopper.
According to the second aspect of the invention, there is provided a fuel injector which comprises: (a) a housing; (b) a control valve disposed movably within the housing to displace a needle for emitting a fuel spray; (c) a large-diameter piston disposed slidabley within the housing; (d) a small-diameter piston disposed slidably within the housing to move the control valve; (e) a displacement amplifying chamber filled with fluid to which the large-diameter piston and the small-diameter piston are exposed, the displacement amplifying chamber working to amplify and transmit displacement of the large-diameter piston to the small-diameter piston; (f) an actuator working to displace the large-diameter piston; (g) a first cylindrical chamber formed in the housing within which the large-diameter piston is disposed; (h) a second cylindrical chamber formed in the housing within which the small-diameter piston is disposed, the second cylindrical chamber communicating with the first cylindrical chamber through the displacement amplifying chamber, a longitudinal center line of the second cylindrical chamber extending eccentrically to a longitudinal center line of the first cylindrical chamber. The small-diameter piston is arranged coaxially with the control valve on one side of the displacement amplifying chamber.
In the preferred mode of the invention, the actuator is implemented by one of a piezoelectric device and a magnetostrictor, the control valve being moved to control fluid pressure within a back pressure chamber to which an end of the needle is exposed for opening a spray hole. The large-diameter piston is arranged coaxially with the actuator on one side of the displacement amplifying chamber. The small-diameter piston is arranged coaxially with the control valve on the other side of the displacement amplifying chamber.
The longitudinal center line of the second cylindrical chamber is shifted a distance e from the longitudinal center line of the first cylindrical chamber. The distance e satisfies a relation of 2e greater than Dxe2x88x92d where D is diameter of the large-diameter piston and d is diameter of the small-diameter piston.
The longitudinal center line of the second cylindrical chamber extends eccentrically to the longitudinal center line of the first cylindrical chamber to define a surface at a junction of the first and second cylindrical chambers which is exposed to the second cylindrical chamber and works as a stopper restricting movement of the small-diameter piston toward the displacement amplifying chamber.
According to the third aspect of the invention, there is provided a fuel injector which comprises: (a) a nozzle needle displaced to open a spray hole; (b) an actuator displacing the nozzle needle, the actuator having a longitudinal center line extending eccentrically to a longitudinal center line of the nozzle needle; and (c) a housing within which the actuator is disposed, the housing being clamped on an internal combustion engine at two points provided symmetrically with respect to a line extending perpendicular to the longitudinal center lines of the nozzle needle and the actuator.
In the preferred mode of the invention, the housing has formed therein a high-pressure passage through which fuel is supplied to the spray hole. The high-pressure passage has a longitudinal center line extending perpendicular to a common line to which the longitudinal center lines of the actuator and the nozzle needle extend perpendicular.